In processing silver halide color photographic materials, used processing solutions are generally discharged as an overflow solution However, since such overflow solution still contains active ingredients, many studies have been conducted on so-called regeneration techniques of utilizing the overflow solution as a replenisher by adding thereto deficient ingredients. Reuse of the overflow solution as a replenisher is preferable not only because running cost is decreased since amounts of chemicals to be used can be decreased in comparison with the case of newly prepared replenishers but because environmental pollution is markedly reduced since the amount of overflow waste is decreased, thus being preferable in view of preservation of the environment, too.
However, it is difficult to develop the technique of regenerating the overflow solution, and regeneration of a bleach-fixing solution has been believed to be particularly difficult. A bleach-fixing solution generally contains at least three chemicals having different functions, i.e., an iron aminopolycarboxylate (III) complex as a bleaching agent, a thiosulfate as a fixing agent, and a sulfite as a preservative. An overflow solution of the bleach-fixing solution further contains silver ions and color developer ingredients brought over from a prebath. In addition, it contains iron aminopolycarboxylate (II). In reusing this solution, there arises delayed desilvering, conversion of a cyan dye to its leuco form (color restoration failure) or undesirable stain (stain or background) due to accumulation of halide ions or silver ions, accumulation of iron aminopolycarboxylate (II), and accumulation of developer ingredients or accumulation of a sulfate produced as a result of the oxidation of the sulfite ion.
In order to solve the above-described problems, various regeneration techniques have been proposed. A technique of bringing a used solution into contact with metallic iron (steel wool) is disclosed, for example, in Radiography, 29, 256-259 (1963), and JP-A-48-2624 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"). In accordance with this technique, the silver ion concentration can be decreased by recovering metallic silver formed by the contact between silver ions and metallic iron, but the oxidizing power of the bleach-fixing solution is reduced since the metallic iron dissolves out as an iron (II) ion having a strong reducing ability, thus desilvering failure or color restoration failure is likely to occur. The possibility of this problem arising increases as the silver ion concentration decreases.
A technique of recovering silver ions by reducing it through electrolysis is described, for example, in JP-A-50-98837, JP-A-51-19535, JP-A-51-36136, and U.S. Pat. No. 4,014,764. In this technique, too, an iron (III) complex is concurrently reduced to an iron (II) complex, or a sulfite ion around a cathode is oxidized to a sulfate ion, thus desilvering failure or color restoration failure is also likely to occur and, at the same time, solution stability is decreased. The above described problems become more serious as the amount of electric current is increased to decrease the iron ion concentration in the bleach-fixing solution by increasing the yield of silver recovery.
A technique of removing the silver complex by adsorbing it with an ion exchange resin is described, for example, in J. Appl. Photogr. Eng. 6, 14-18 (1980), SMPTE J, 93, 800-807 (1984). However, this technique requires the liberation of the adsorbed iron complex from the resin for regeneration of the resin. Hence, procedures for effecting the technique are complicated, and a large amount of waste liquor is produced. Thus, this technique is not satisfactory in view of running cost.
JP-A-48-49437 and JP-A-50-145231 disclose a technique of regenerating the overflow solution by decreasing the equilibrium accumulation amount of silver ion through dilution or the like without positively removing silver. This technique is simple and less costly because no special desilvering apparatuses are required. In this technique, however, the accumulation of silver halide dissolved from the light-sensitive material, particularly dissolved silver bromide is present in a large amount, and the accumulation of sulfate delays desilvering. In addition, the accumulation of developer ingredients causes undesired stain and tends to cause color restoration failure. Thus, this technique involves problems as to the stability of running properties.